1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to a bit recording process on a ferroelectric medium using a probe or a small conductive structure and a recording medium thereof, in which a bit size can be decreased to increase data recording density as well as to reduce losses occurring to reproduction signals.
2. Description of the Prior Art
In response to booming Internet-related technologies, various record media capable of storing a massive amount of data including dynamic images have been developed. In addition, user demands to freely use data stored in such record media while moving are an important factor that drives a next generation information storage market. Not only the record media capable of storing a massive amount of data but also means for reading the data from the record media are essential in the information storage media market.
To date, portable non-volatile data storage devices generally include solid-state memory devices such as flash memories and disk-type memory devices such as hard disks. The solid-state memory devices are expected to have a recording capacity up to about several giga bytes GB in several years, but still can hardly be used as massive data record storage devices. However, it is still expected that the solid-state memory devices will be used as memory devices for high-speed operations in present personal computers, and the hard-disk type memory devices will be used for main storage devices.
A common magnetic hard disk mounted on a portable device is expected to have a capacity of about 20 giga bytes in the near future. However, it is also expected difficult to obtain higher magnetic recording density owing to “superparamagnetism.”
Recent approaches are introducing new memory devices which use a scanning probe as recording and reproducing means and a ferroelectric medium as a record medium.
According to such a technology using a scanning probe or Scanning Probe Microscopy (SPM) technology, it is possible to probe a microscopic area of several to tens of nano-meters with the scanning probe. Furthermore, the ferroelectric medium used as the record medium is not influenced by superparamagnetism unlike magnetic storage media. Accordingly, it is possible to increase recording density of SPM memory devices over the magnetic record media.
However, memory devices introduced to date, in particular, which use a ferroelectric medium as a data-recording material layer have a drawback in that the bit size is limited by a probe and a recording process causes variations in surface potential (reproduction signals).
That is, in the related art, when bits are recorded on a ferroelectric medium in the form of a thin film, it is impossible to record bits at a size smaller than that of a probe (P. Paruch et al., Appl. Phys. Lett. 79, 530 (2001)). Moreover, the probe remaining in a contact state right after a recording operation disadvantageously changes potential which is used as reproduction signals in a probe data storage device.